Gaseous laser systems with edge-defining element and related techniques

ABSTRACT

Gaseous laser systems and related techniques are disclosed. Techniques disclosed herein may be utilized, in accordance with some embodiments, in providing a gaseous laser system with a configuration that provides (A) pump illumination with distinct edge surfaces for an extended depth and (B) an output beam illumination from a resonator cavity with distinct edges in its reflectivity profile, thereby providing (C) pump beam and output beam illumination on a volume so that the distinct edge surfaces of its pump and beam illumination are shared-edge surfaces with (D) further edge surfaces of the amplifier volume at the surfaces illuminated directly by the pump or output beams, as defined by optical windows and (optionally) by one or more flowing gas curtains depleted of the alkali vapor flowing along those optical windows. Techniques disclosed herein may be implemented, for example, in a diode-pumped alkali laser (DPAL) system, in accordance with some embodiments.

FIELD OF THE DISCLOSURE

The present disclosure relates to laser systems and more particularly toflowing gas amplifier laser systems, such as diode-pumped alkali laser(DPAL) systems.

BACKGROUND

Diode-pumped lasers typically employ laser diodes as the pump beamsource. Some of these lasers, such as diode-pumped alkali lasers(DPALs), employ a gaseous lasing medium including an alkali metal vapor.Diode pumping can be provided in a longitudinal manner (i.e., pump lightenters the lasing medium through a surface that is shared with theoutput beam) or a transverse manner (e.g., pump light enters the lasingmedium through a surface that is not shared with the output beam).

SUMMARY

The subject matter of this application may involve, in some cases,interrelated products, alternative solutions to a particular problem,and/or a plurality of different uses of a single system or article.

One example embodiment provides a gaseous laser system. The gaseouslaser system includes an unstable resonator. The gaseous laser systemalso includes a lasing amplifier disposed in an optical pathway of theunstable resonator, wherein the lasing amplifier includes an opticalwindow assembly through which a flowing lasing gas passes in operationof the gaseous laser system. The gaseous laser system also includes apump beam source configured to emit a pump beam including pump light.The gaseous laser system also includes an edge-defining elementconfigured to define an edge of the pump light such that a resultantpump beam is delivered to the flowing lasing gas in the lasingamplifier.

In some cases, the edge-defining element includes a mirror assemblydisposed near an intersection of the pump beam and the optical pathwayof the unstable resonator and configured to have the pump beam incidenttherewith. In some instances, the mirror assembly is configured toreflect at least a portion of the pump beam so as to define the edge ofpump light incident therewith.

In some cases, the edge-defining element includes an assembly of opticalelements disposed outside of the optical pathway of the unstableresonator and configured to have the pump beam pass therethrough. Insome instances, the assembly of optical elements is configured to atleast one of refractively optically transport and reflectively opticallytransport at least a portion of the pump beam so as to define the edgeof pump light incident therewith. In some instances, the assembly ofoptical elements is configured to form an image of at least a portion ofthe pump beam so as to define the edge of pump light incident therewith.

In some cases, the gaseous laser system is configured to have at leastone flowing gas curtain pass over an interior surface of the opticalwindow assembly in a region through which the pump beam passes inoperation of the gaseous laser system. In some instances, the at leastone flowing gas curtain includes an inactive gas. In some instances, theat least one flowing gas curtain is configured to have the pump beamincident therewith so as to define the edge of pump light incidenttherewith.

In some cases, the pump beam source is configured for longitudinalpumping of the lasing amplifier. In some other cases, the pump beamsource is configured for transverse pumping of the lasing amplifier. Insome cases, the gaseous laser system is configured as a diode-pumpedalkali laser (DPAL), and the flowing lasing gas includes a vapor of analkali metal.

Another example embodiment provides a method of optically pumping agaseous laser system. The method includes emitting a pump beam includingpump light. The method also includes defining an edge of the pump light.The method also includes delivering a resultant pump beam to a flowinglasing gas of the gaseous laser system.

In some cases, defining the edge of the pump light involves a reflectionprocess. In some instances, the reflection process includes reflectingat least a portion of the pump beam off a mirror before delivering theresultant refined pump beam to the flowing lasing gas.

In some cases, defining the edge of the pump light involves at least oneof a refractive optical transport process and a reflective opticaltransport process. In some instances, the at least one of the refractiveoptical transport process and the reflective optical transport processincludes focusing the pump beam through at least one lens beforedelivering the resultant pump beam to the flowing lasing gas.

In some cases, in delivering the resultant pump beam to the flowinglasing gas, the resultant pump beam passes through at least one flowinggas curtain provided adjacent to the flowing lasing gas. In someinstances, the at least one flowing gas curtain includes an inactivegas.

In some cases, emitting the pump beam involves a longitudinal pumpingprocess in which the pump beam and an output beam of the gaseous lasersystem are transmitted through at least one shared optical window. Insome other cases, emitting the pump beam involves a transverse pumpingprocess in which the pump beam and an output beam of the gaseous lasersystem are transmitted through different optical windows. In some cases,the gaseous laser system is configured as a diode-pumped alkali laser(DPAL), and the flowing lasing gas includes a vapor of an alkali metal.

Another example embodiment provides a gaseous laser. The gaseous laserincludes a gain medium with an interior volume within the substance ofthe gain medium that is illuminated by one or more pump laser source(s)entering the volume. The gaseous laser also includes edge surfaces fullyenclosing the interior volume where the gain of the medium changes froma low value to a high value. The gaseous laser further includes one ormore pump light sources whose illumination of the interior volume of thegain medium has an intensity distribution in the plane perpendicular toits direction of propagation that is configured to transition abruptlyfrom low to high intensity (e.g., the edge of the pump beam), therebydelineating one or more edge surfaces of the gain medium, where thetransition in pump illumination defines that surface.

In some cases, the gaseous gain medium is flowing so that thestreamlines of the flow define planes that are also edge surfaces wherethe gain of the medium changes from a low value to a high value, and oneor more additional surface of the gain medium are defined by the edge ofthe pump beam (i.e., a spatially abrupt transition in pump lightintensity).

In some cases, the configuration is one of longitudinal pumping (e.g.,pump light enters the gain medium through a surface that is shared withthe output beam), the surfaces where the pump beam and output beam crossthe medium boundary and enter/exit the medium are defined by flowstreamlines along the windows, with or without a flowing inactive gascurtain, and the perimeter surface enclosing and defining the pumpregion in the plane perpendicular to the pump beam and output beam isdefined at least partially by a spatially abrupt transition in pumplight intensity (e.g., the edge of the pump beam). In some suchinstances, the illumination pattern of the laser output beam formed bythe unstable resonator (e.g., the magnified image of the output couplingmirror reflected from the high-reflectivity mirror) coincides with theperimeter surface that encloses the pumped region.

In some cases, the configuration is one of transverse pumping (e.g.,pump light enters the gain medium through a surface that is not sharedwith the output beam), the surface(s) where the pump beam crosses themedium boundary and enters the medium are defined by flow streamlinesalong the windows, with or without a flowing inactive gas curtain, thesurface(s) where the output beam crosses the medium boundary andenters/exits the medium are defined by flow streamlines along thewindows, with or without a flowing inactive gas curtain, and theperimeter defining the pump region along the gas flow direction isdefined at least partially by a spatially abrupt transition in pumplight intensity. In some such instances, the illumination pattern of theoutput beam formed by the unstable resonator (e.g., the magnified imageof the output coupling mirror reflected from the high-reflectivitymirror) coincides with the rectilinear surface that encloses the pumpedregion.

In some cases, the illumination pattern of the pump beam within thepumped region is approximately uniform. In some cases, the illuminationtransition from low to high intensity (e.g., the edge of the pump beam)is more narrowly defined using a mirror, thereby confining pump light tobe inside the medium boundary that otherwise would diverge beyond thesurface of the gain region. In some cases, the mirror placement confinesthe pump light to a circular, polygonal, rectangular, oval, or circularillumination pattern. In some cases, the mirror placement confines thepump light to a rectangular illumination pattern. In some cases, theplacement of lenses confines the pump light to a rectangularillumination pattern. In some cases, the flow defines the amplifiermedium substance with planar edge surfaces including windows and/orflowing gas curtains, where the output beam includes parallel rays witha perimeter defined by the geometry of the unstable resonator, and thepump beam is tailored to have abrupt edges so that the amplifier gainmedium includes the volumetric intersection of the flowing lasing gas,the pump beam, and the output beam.

In some cases, the pump source is oriented such that the edge of itsillumination along the fast-axis direction, which has lower divergenceand better spatial definition than that of its slow axis, is directed soas to define one or more edge surfaces of the pump light along the gasflow direction, thereby forming one or more edges of the interior volumeof the gain medium for an extended depth at the lasing gas flow entranceand exit.

The features and advantages described herein are not all-inclusive and,in particular, many additional features and advantages will be apparentto one of ordinary skill in the art in view of the drawings,specification, and claims. Moreover, it should be noted that thelanguage used in the specification has been selected principally forreadability and instructional purposes and not to limit the scope of theinventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a gaseous laser system configured for longitudinalpumping, in accordance with an embodiment of the present disclosure.

FIG. 2 illustrates a partial view of the system of FIG. 1 , inaccordance with an embodiment of the present disclosure.

FIG. 3 illustrates another partial view of the system of FIG. 1 , inaccordance with an embodiment of the present disclosure.

FIG. 4A is a graph illustrating reflectivity as a function of positionfor an output coupler configured with graded reflectivity, in accordancewith an embodiment of the present disclosure.

FIG. 4B is a graph illustrating reflectivity as a function of positionfor an output coupler configured with uniform reflectivity, inaccordance with an embodiment of the present disclosure.

FIG. 5 illustrates another partial view of the system of FIG. 1 , inaccordance with an embodiment of the present disclosure.

FIG. 6 illustrates an example arrangement of pump beam source(s) andbeam-shaping optic(s), in accordance with an embodiment of the presentdisclosure.

FIG. 7 illustrates an example arrangement of pump beam source(s) andbeam-combining optic(s), in accordance with an embodiment of the presentdisclosure.

FIG. 8 illustrates an example longitudinal pumping arrangement, inaccordance with an embodiment of the present disclosure.

FIG. 9 illustrates an example longitudinal pumping arrangement, inaccordance with an embodiment of the present disclosure.

FIG. 10 illustrates a gaseous laser system configured for transversepumping, in accordance with an embodiment of the present disclosure.

FIG. 11 illustrates a partial view of the system of FIG. 10 , inaccordance with an embodiment of the present disclosure.

FIG. 12A illustrates an existing approach to pump beam intensitydistribution for an existing DPAL system.

FIGS. 12B-12E illustrate several example pump beam intensitydistributions in accordance with some embodiments of the presentdisclosure.

These and other features of the present embodiments will be understoodbetter by reading the following detailed description, taken togetherwith the figures herein described. In the drawings, each identical ornearly identical component that is illustrated in various figures may berepresented by a like numeral. For purposes of clarity, not everycomponent may be labeled in every drawing. Furthermore, as will beappreciated in light of this disclosure, the accompanying drawings arenot intended to be drawn to scale or to limit the described embodimentsto the specific configurations shown.

DETAILED DESCRIPTION

Gaseous laser systems and related techniques are disclosed. Techniquesdisclosed herein may be utilized, in accordance with some embodiments,in providing a gaseous laser system with a configuration that provides(A) pump illumination with distinct edge surfaces for an extended depthand (B) an output beam illumination from a resonator cavity withdistinct edges in its reflectivity profile, thereby providing (C) pumpbeam and output beam illumination on a volume so that the distinct edgesurfaces of its pump and beam illumination are shared-edge surfaces with(D) further edge surfaces of the amplifier volume at the surfacesilluminated directly by the pump or output beams, as defined by opticalwindows and (optionally) by one or more flowing gas curtains depleted ofthe alkali vapor flowing along those optical windows. Techniquesdisclosed herein may be implemented, for example, in a diode-pumpedalkali laser (DPAL) system, in accordance with some embodiments.Numerous configurations and variations will be apparent in light of thisdisclosure.

General Overview

Diode-pumped alkali lasers (DPALs) offer a promising technology forimplementing a single-aperture beam with favorable characteristics.Since a DPAL is a gas laser, it does not suffer from many of the powerlimitations of solid lasers, such as thermal lensing. The transitions ofinterest are in the near-infrared, which is shorter in wavelength thanexisting approaches, so that the diffraction-limited output beam maypropagate a greater distance for a given divergence. The differencebetween the energy of the pump photon and the output beam photon—thequantum defect energy between the P3/2 and P1/2 levels—is only of ordera couple percent of their average, offering the potential for very highoptical-to-optical conversion efficiencies.

Alkali atoms cycle among three levels to convert pump photons to beamphotons. They are (i) resonantly pumped to the second excited state (theP3/2 level), (ii) collisionally quenched to the lasing state (the P1/2level), and then (iii) transition to the ground state (the S1/2 level),thereby delivering amplification to the output beam. In the limit ofvery high pump and output beam intensity, and with high collisionalquenching rate, the cycle rate can far exceed the natural decay rateassociated with maintaining a continuous population in the P-states. Inthis limit, the optical-to-optical efficiency approaches the quantumdefect fraction (i.e., the difference between the P3/2 and P1/2 levelenergies divided by their average) of a couple percent. However, thereis also a threshold that must be overcome—the pump beam must havesufficient intensity to “bleach” the levels, achieving the populationinversion that is required before lasing begins. Due to the constantrate of natural spontaneous decay of the excited states, this penalty tothe optical-to-optical efficiency is always present at a constant energyloss rate. In some configurations, the output beam in the amplifierregion exceeds the pump intensity. Consequently, the higher the pumpintensity that is achieved above lasing threshold, the greater theportion of the pump beam that can be converted to output beam.

These considerations have led practitioners to design and implement DPALpump illumination distributions that seek high efficiency byconcentrating the pump light to maximize the pump intensity. Similarlogic applies to concentrating the intensity of the output beam in theregion where the pump light is most intense. For example, consider FIG.12A, which illustrates an existing approach to pump beam intensitydistribution for an existing DPAL system. Here, the pump beam intensityimpinges on a flowing lasing gas as a function of position alongone-dimension (e.g., the slow-axis dimension of a pump array consistingof several diode array bar stacks). As can be seen, the pump beamintensity is maximized in the center and made as spatially narrow aspossible. This illumination pattern may be accomplished, for example, byinclining several diode array bar stacks so that their central rays meetat the same spot when they reach the flowing lasing gas. Thedistribution may have different widths along the vertical and horizontaldirections, which may be associated with the fast and slow axes of thepump array. After collimation by a fast-axis collimating lens, thepropagation in the fast axis has very low divergence, so that theillumination pattern along this direction is determined primarily by theheight of the stack and directional pointing. The propagation in theslow axis, however, has much larger divergence. Constraining thedimension of the spatial illumination pattern along the slow axis hasled to the perceived requirement that the pump laser stacks bepositioned close to the amplifier region. Increasing the number ofstacks illuminating the amplifier region while maintaining proximityresults in placing the stack arrangement to fill a conical pattern outto angles that approach 45°. The convergence of these paths is optimallyplaced at the center of the amplifier, diverging rapidly withdisplacement from the center and decreasing in intensity away from thiscentral point. Consequently, the depth of the amplifier region has beenlimited to only a few centimeters.

This existing strategy which maximizes the pump intensity within a smallregion does not lead to maximum performance of the full system. On anatomic level, the cycle rate depends not only on the pump intensity, butalso the quenching rate between the P3/2 and P1/2 levels, and the lasingbeam intensity. Each atom can absorb a pump beam photon only as fast asit can deliver it to the output beam. The quenching rate is uniform,being determined by the pressure of the helium buffer/quenching gas andthe partial pressure of any (optional) hydrocarbon or fluorocarbonmolecular quenching agent. Then, on a local level, full absorption ofthe pump beam depends on the optical thickness: the concentration of thealkali atoms (in the absorbing ground state) times the physicalthickness of the medium. However, if the pump beam has an intensitymaximum, then it also will have regions where the intensity drops offwith distance from that maximum. Unfortunately, the optimal choice ofoptical thickness also drops with distance. For an operating DPAL, it isnot feasible to vary the optical thickness. The amplifier region in sucha system must be chosen with a single alkali vapor concentration that isa compromise between the choice that would be optimal for the region ofgreatest pump intensity and the regions with lesser pump intensity. Sucha compromise can result in the pump beam penetrating completely throughthe gain medium in regions where it is most intense, while regions ofthe amplifier where the pump beam is less intense have alkaliconcentrations that are unfavorably high. As the pump beam attenuatespassing through the amplifier in these regions, it may not even exceedlasing threshold near the rear of the amplifier.

The output beam is generally formed in a resonator—a cavity with twomirrors (i.e., a high-reflectivity mirror and an output coupler mirror)that define the output beam direction. An unstable resonator ischaracterized by a magnification whose absolute value exceeds unity. Asthe beam reflects between the mirrors, the illumination pattern ismagnified so that power escapes outside the perimeter of the outputcoupling mirror. The illumination pattern returning to thehigh-reflectivity mirror from the output coupler is defined by thereflectivity profile of the output coupler, which drops to zeroreflectivity at its perimeter. After reflecting off the output coupler(and optionally passing through an intermediate focus), the beamdiverges while passing back through the amplifier medium, reaching itsmaximum transverse size as it reaches the high-reflectivity mirror.After reflecting off that mirror, the magnified beam becomes parallel,with an intensity profile and a perimeter defined by the magnifiedreflectivity and perimeter of the output coupler. As it passes throughthe amplifier medium, each region of the beam has its intensity modifiedaccording to the localized gain of the region it is passing through.Once it passes beyond the output coupler, the output beam consists of anannulus defined by the magnified beam pattern minus the reflectedintensity removed from the central region. Since the central region maybe only partially reflective, some fraction of the output power can passthrough.

The size and shape of the perimeter of the unstable resonator cavityelements (e.g., the output coupler) can be chosen to achieve a giventarget performance of the DPAL. The size and shape of these elements maybe chosen, for example, to extract beam from the pumped region and toavoid sending the output beam through regions of the flowing lasing gasthat do not have sufficient pump intensity to achieve a populationinversion. The optional choice of pump beam perimeter size and shape isa compromise if the pump intensity tapers from a maximum intensity(where excess pump beam penetrates through the amplifier mediumthickness and emerges out the back under-utilized) to a lower intensity(where insufficient pump beam intensity is exhausted midway, leaving therearmost layer of the amplifier medium without a population inversion).Indeed, if the cavity elements are chosen so that the output beam is toolarge, much of the output beam may be forced to propagate throughregions of the amplifier medium with negative gain (i.e., attenuation).

The dimensions of the amplifier region, combined with the localpopulation inversion, determine not only the gain through the systemalong the path of the output beam, but also provide gain in otherdirections. Spontaneous emission from either the P3/2 or P1/2 state tothe S1/2 ground state is directionally isotropic and can be amplifieddue to the population inversions that are present in the system. Thisso-called amplified spontaneous emission (ASE) is a power loss mechanismthat depletes the population inversions. Since the gain is exponential,the power out the sides of the amplifier medium becomes significant ifthe spatial size of the amplifier medium transverse to the beamdirection (significantly) exceeds its dimension along the beam. Theratio of the dimension along the beam path to the transverse dimensionis often termed the dimensional “aspect ratio.” Current practice islimited to aspect ratios of approximately 1:2 (i.e., one-half).

Thus, and in accordance with some embodiments of the present disclosure,gaseous laser systems and related techniques are disclosed. Techniquesdisclosed herein may be utilized, in accordance with some embodiments,in providing a gaseous laser system with a configuration that provides(A) pump illumination with distinct edge surfaces for an extended depthand (B) an output beam illumination from a resonator cavity withdistinct edges in its reflectivity profile, thereby providing (C) pumpbeam and output beam illumination on a volume so that the distinct edgesurfaces of its pump and beam illumination are shared-edge surfaces with(D) further edge surfaces of the amplifier volume at the surfacesilluminated directly by the pump or output beams, as defined by opticalwindows and (optionally) by one or more flowing gas curtains depleted ofthe alkali vapor flowing along those optical windows. Techniquesdisclosed herein may be implemented, for example, in a diode-pumpedalkali laser (DPAL) system, in accordance with some embodiments.

In accordance with some embodiments, systems disclosed herein may beconfigured, for example, with a gaseous laser with a flowing lasing gas(i.e., amplifier medium) that is optically pumped with diode laserarrays in an unstable resonator to form a single collimated output beam.In accordance with some embodiments, at least two of the surfaces of theamplifier volume may be defined by optical windows and (optionally) oneor more flowing gas curtains such that the flowing lasing gas itselfdoes not extend beyond those boundaries. In accordance with someembodiments, definition of the edge surfaces of (i) the pump beam and(ii) the output beam and co-locating those surfaces with one anotherand/or the edge surfaces of (iii) the flowing lasing gas may contributeto improvements in efficiency and power-in-bucket metrics.

In accordance with some embodiments, techniques disclosed herein mayinvolve, for example, spatially matching laser pump illumination withthe flowing lasing gas and unstable resonator beam formation geometries.In accordance with some embodiments, techniques disclosed herein mayinvolve, for example, defining the edge surfaces of the amplifier volumeand co-locating those surfaces wherever possible with the edge surfacesof (i) the pump beam, (ii) the output beam, and (iii) the flowing lasinggas.

In accordance with some embodiments, techniques disclosed herein mayinvolve arranging pump laser(s) to have a sharp cutoff in the gas flowdirection and making that edge surface substantially identical with theoutput beam, also with a sharp cutoff. As will be appreciated in lightof this disclosure, that sharp cutoff may be achieved, for example,using the fast-axis edge of the pump laser beam, in accordance with someembodiments. If there is no optical transport, it still may provide asufficiently sharp edge. Also, if there is no optical transport, theslow axis may be smeared out, and it may be desirable to utilize an endmirror, though that may impact the ability to achieve sufficientintensity. If, however, there is optical transport, then sufficientintensity above threshold may be achieved, for example, by concentratingthe light in the fast-axis direction. This may be accomplished, forexample, with a focusing pair (e.g., an afocal telescope).

In accordance with some embodiments, techniques disclosed herein may beimplemented, for example, in a gaseous laser system (e.g., DPAL system)configured for longitudinal pumping. In such cases, the pump and outputbeams generally may define the x-y profile forming a given shape (e.g.,square, rectangle, octagon, circle, etc.), while the z-direction may bedelimited by optical windows and (optionally) flowing gas curtains whereboth beams come through. In accordance with some other embodiments,techniques disclosed herein may be implemented, for example, in agaseous laser system (e.g., DPAL system) configured for transversepumping. In such cases, the edges of both the pump and output beamsgenerally may define the gas inflow and outflow boundaries of theamplifier regions, and optical windows and (optionally) flowing gascurtains generally may define all sides (e.g., four sides), togetherwith a co-located edge of one of the beams (either pump or output). Inat least some instances, the gas inflow and outflow boundaries along thegas flow direction generally may be due to the edge(s) of both the pumpand output beams, in accordance with some embodiments. In at least someinstances, at least one of the edges may be defined along the directionof the fast axis of the pump laser, which offers better definition inits spatial and angular distribution, thereby defining an edge surfacefor an extended depth. In accordance with some embodiments, techniquesdisclosed herein may be used to provide a DPAL system configured toilluminate a sharp cutoff at an edge surface in the gas flow direction.

As will be appreciated in light of this disclosure, recognizing theimportance of definition and co-location of the edges of the pump andoutput beams with one another and with the edges of the amplifier for anextended depth runs counter to existing thinking and approaches. Someexisting approaches include considerations for an output coupling opticwith tapering reflectivity, intended to reduce the definition of theedge of the output beam (i.e., make it vaguer). Also, some existingapproaches include considerations to reflect back into the amplifiermedium that portion of the pump power from the central region of highestintensity that penetrates through the amplifier medium for a second passto harvest its power, which is evidence that it was not optimized in theoriginal design of such existing approaches. More specifically, someexisting approaches seek to reduce pump beam spot size by adding customprisms, angled in quadrants, that deflect beams that emanate from outerstripes on each bar inward toward the center along the slow axis anddeflect beams that emanate from the outer bars on the diode array stackinward toward the center along the fast axis. The angled pump arraysproduce a pumped gain region which has a spatial waist in the center ofthe amplifier region and grows transversely moving axially, towards thefront and rear. For much of the amplifier length along the beam, thewidth exceeds the length, resulting in appreciable amplified spontaneousemission (ASE). Thus, an increase of either of these dimensions iscounterintuitive. Regarding the output beam in a transversely pumpedarrangement, some existing approaches have utilized a polygonal outputcoupler without concomitant considerations given to defining amplifiersurfaces coinciding with that polygonal boundary, resulting in pumpedregions with no stimulated emission from the output beam cavity. Someexisting approaches also suffer from much of the output beam passingthrough regions of negative gain, especially near the perimeter, asdescribed above.

Contrary to these existing approaches, and as disclosed herein, it maybe desirable, at least in some instances, to achieve a pump beamintensity that is (A) uniformly high (B) in a given pattern/shape (C)out to well-defined edges (D) for an extended depth, in accordance withsome embodiments. To accomplish this, it may be desirable, at least insome instances, to transport the pump beam's fast-axis light such thatit illuminates a well-defined portion of the amplifier region such thatthe edge of that fast-axis illumination defines one or more edgesurfaces for an extended depth. Another approach to that end is, inaccordance with some embodiments, to de-magnify the pump beam lightalong the fast axis with an optical transport, concentrating its power.As the divergence of the fast and slow axes may differ, for instance, bya factor of one hundred, the increase in the fast-axis divergence thatmay result from this concentration of power still may permit thefast-axis illumination to sufficiently define an edge surface for anextended depth. Another approach is, in accordance with someembodiments, to magnify the slow-axis pump light with an opticaltransport, to increase its spatial size while reducing its divergence.This approach may allow the slow-axis light to provide improveddefinition of edge surfaces for an extended depth. While expanding theslow-axis light and maintaining pump intensity may require furthercompression of fast-axis light, this approach may provide a pump beamthat has divergence along the slow axis that more closely matches thatof the fast axis, so that the pump beam may propagate through anextended amplifier region while maintaining well-defined edge surfacesto a greater depth along both axes as closely as possible. As will beappreciated in light of this disclosure, some combination of theseapproaches may be utilized together to achieve a target pump intensityand spatial profile as a function of depth, in accordance with someembodiments. Furthermore, to allow significant de-magnification alongthe fast-axis direction while still achieving high intensity and a pumpbeam size along the fast axis comparable to that along the slow-axisdirection, a design utilizing a pump beam source with a very asymmetricshape (e.g., a stack of many bars) may be desirable (at least in somecases), in accordance with some embodiments.

Another approach is to confine the slow-axis pump light with edgemirrors, in accordance with some embodiments. A pump light illuminationpattern having a generally circular or polygonal shape may be provided,in accordance with some embodiments, by using the high-spatialdefinition of the fast-axis light to define the edge while diffusing thelight propagating toward the center. In accordance with someembodiments, this arrangement may be augmented, for example, with acircumscribing mirror (or mirror array) to constrain stray or divergentpump light and reflect it back within the perimeter. In accordance withother embodiments, this arrangement may be augmented with a spatiallydefining mask, to absorb the tails of the pump beam, preventing themfrom delivering heat to the amplifier region, if their trajectory wouldprevent them from contributing to the output beam anyway.

As will be further appreciated in light of this disclosure, techniquesdisclosed herein may involve one or more generally counterintuitiveconcepts. For example, rather than incorporating elements and systemrefinements that narrow the spatial distribution of the pump light, likedescribed above in relation to the prior art of FIG. 12A, techniquesdisclosed herein may be used to expand the slow-axis spatialdistribution, reduce its divergence, and improve its delineation of awell-defined edge surface for an extended depth, even if they broadenthe spatial distribution of pump light illumination on the flowinglasing gas, in accordance with some embodiments. That edge surface ofthe pump beam then may serve as the choice for the edge surface of theoutput beam, which, together with amplifier edges accomplished by theoptical windows (or gas curtains flowing along the optical windows),then may determine the size and shape of the amplifier region, inaccordance with some embodiments. In turn, this may determine the sizeand shape of the perimeter of the output coupling optic, in accordancewith some embodiments.

In accordance with some embodiments, techniques disclosed herein may beutilized to provide a highly desirable configuration for pumping a DPALwith a uniform intensity. As will be appreciated in light of thisdisclosure, efficient pumping of a DPAL may involve illuminationintensities of a few kilowatts per square centimeter, but typical diodestacks may produce closer to only 200 W/cm². Rather than overlappingpump beams from various angles to achieve, for instance, a ten-foldincrease in intensity, techniques disclosed herein may utilize opticaldemagnification (e.g., approximately ten-fold) along the fast-axis,optionally with a beam-combining element that may allow tiling theamplifier surface with a tessellated pump beam that is still collimatedalong the fast axis, in accordance with some embodiments. By(optionally) choosing the edges of this beam along the fast axis to liealong the flow direction, the pump beam edge surface may be shared bythe output beam edge, in accordance with some embodiments. By largelypreserving the fast-axis collimation, the amplifier region may be pumpedfrom both sides without the two pump arrays jeopardizing one another, solong as a small angle is introduced between the impinging beam axes, inaccordance with some embodiments. By using two-sided pumping, themagnification of each pump beam may be reduced (e.g., by half, such thatthere is a five-fold concentration rather than ten-fold), in accordancewith some embodiments. The slow-axis direction then may be defined, inaccordance with some embodiments, by using an optical method to createan image within the amplifier or by using side mirrors to contain theslow-axis light, either optionally being augmented by a flowing sidewindow to assist in defining the side surfaces of the amplifier region.The depth of the amplifier region then may approach or exceed thetransverse dimension, reaching an aspect ratio that approaches orexceeds unity, in accordance with some embodiments.

As will be appreciated in light of this disclosure, techniques disclosedherein may be used, in part or in whole, to improve any of a wide rangeof existing DPAL systems. For example, in accordance with someembodiments, techniques disclosed herein may be utilized in relation toa DPAL system like that described in U.S. Pat. No. 9,653,869, titled“Optical Surface Preservation Techniques and Apparatus,” the disclosureof which is herein incorporated by reference in its entirety.

Longitudinally Pumped System Architecture and Operation

FIG. 1 illustrates a gaseous laser system 1000 a configured forlongitudinal pumping, in accordance with an embodiment of the presentdisclosure. As can be seen, system 1000 a may include an unstableresonator 100 including a high-reflectivity mirror 110 and an outputcoupler 120, a lasing amplifier 130, and an optical window assembly 140.As can be seen further, system 1000 a may include one or more pump beamsources 150, together with one or more beam-shaping optics 190 (for thefast and slow axes), and a pump beam edge-defining element 160 (e.g.,such as a mirror, optical element, and/or mask assembly) forlongitudinal pumping of lasing amplifier 130 via one or more pump beams152 through a window assembly 140 (e.g., a forward end window 142 and/ora rearward end window 144) to illuminate the front and/or rear of aflowing lasing gas 170 (e.g., gain medium). In its operation, system1000 a may produce one or more output beams 10. Each of these elementsis discussed in turn below.

As noted above, system 1000 a may include an unstable resonator 100 anda lasing amplifier 130. FIG. 2 illustrates a partial view of system 1000a, in accordance with an embodiment of the present disclosure. In someembodiments, unstable resonator 100 may be configured, for example, as aconfocal unstable resonator. In some cases, unstable resonator 100 maybe configured as a negative branch confocal unstable resonator or apositive branch confocal unstable resonator. Other suitableconfigurations for unstable resonator 100 will depend on a given targetapplication or end-use and will be apparent in light of this disclosure.

Regarding high-reflectivity mirror 110 (of unstable resonator 100), thegeometry and dimensions, as well as the reflectivity, thereof may becustomized, as desired for a given target application or end-use. Insome cases, mirror 110 may have a substantially spherical or parabolicgeometry. In some cases, mirror 110 may have a reflectivity, forexample, in the range of about 95.0-99.9999% (e.g., about 95.0-97.0%,about 97.0-99.0%, about 99.0-99.9999%, about 99.95-99.9999%, or anyother sub-range in the range of about 95.0-99.9999%). In at least somecases, mirror 110 may include and optionally extend beyond theillumination pattern provided by any reflective region of output coupler120, multiplied by the magnification of unstable resonator 100. Othersuitable configurations for high-reflectivity mirror 110 will depend ona given target application or end-use and will be apparent in light ofthis disclosure.

Regarding output coupler 120 (of unstable resonator 100), the geometryand dimensions, as well as the reflectivity, thereof also may becustomized, as desired for a given target application or end-use. Insome embodiments, output coupler 120 may include, for example, (1) aninner region including an output coupling mirror with at least somereflectivity and (2) an outer region (e.g., its perimeter) thatmaximizes transmission. In some such cases, the output coupling mirror(of output coupler 120) may have a substantially spherical or parabolicgeometry. In some cases, the output coupling mirror (of output coupler120) may have a reflectivity, for example, in the range of about50.0-99.9999% (e.g., about 50.0-70.0%, about 70.0-90.0%, about90.0-99.0%, about 99.0-99.9999%, or any other sub-range in the range ofabout 50.0-99.9999%). In some instances, it may be desirable to have areflectivity that transitions smoothly from high reflectivity to hightransmission. In some instances, it may be desirable to ensure thatoutput coupler 120 has a well-defined edge. As will be appreciated inlight of this disclosure, comparing (A) the full width at half maximum(FWHM) (i.e., the distance from one side to the other where theintensity drops to half of its central intensity) and (B) the full widthat one-tenth maximum (FWTM) (i.e., which quantifies the distance betweenthe two side where the intensity has dropped to one-tenth its centralvalue) may provide a measure of the edge thickness. For aone-dimensional Gaussian distribution, the FWTM is 83% greater than theFWHM. For a distribution whose intensity distribution is made moreuniform than a Gaussian and whose edges are better defined than that ofa Gaussian, the FWTM is closer in value to the FWHM. Rather than theFWTM being 83% greater than the FWHM, it may be only 20% greater or evenwithin 0.001-10.0% of the FWHM. The closer the FWTM distance is to theFWHM distance, the sharper the edge definition.

Further regarding the reflectivity of output coupler 120, FIG. 4A is agraph illustrating reflectivity as a function of position for an outputcoupler 120 configured with graded reflectivity, in accordance with anembodiment of the present disclosure, and FIG. 4B is a graphillustrating reflectivity as a function of position for an outputcoupler 120 configured with uniform reflectivity out to a well-definededge, in accordance with an embodiment of the present disclosure. Aswill be appreciated in light of this disclosure, the examplereflectivity profiles shown in FIGS. 4A-4B may be interpreted (A) asbeing across the diameter of an output coupler 120 configured as anaxially symmetric mirror with a circular perimeter or (B) as a functionof two orthogonal axes of an output coupler 120 with a rectangular orsquare perimeter. If output coupler 120 has a graded reflectivity, forexample, then output beam 10 leaving mirror 110 and passing throughflowing lasing gas 170 (discussed below) may have a generally diffuseedge, in accordance with some embodiments. If output coupler 120 insteadhas a uniform reflectivity out to a well-defined edge, for example, thenoutput beam 10 leaving mirror 110 and passing through flowing lasing gas170 still may have a diffuse edge, but only if the gain of flowinglasing gas 170 tapers to zero, in accordance with some embodiments. If,for example, output coupler 120 has a uniform reflectivity and flowinglasing gas 10 has uniform gain due to being pumped with pump beam(s) 152having a distinct edge co-located at the edge of output beam 10, thenoutput beam 10 leaving mirror 110 and passing through flowing lasing gas170 may have a distinct edge, in accordance with some embodiments. Othersuitable configurations for output coupler 120 will depend on a giventarget application or end-use and will be apparent in light of thisdisclosure.

In accordance with some embodiments, lasing amplifier 130 may include awindow assembly 140 in which a flowing lasing gas 170 may be provided.Lasing amplifier 130 further may be configured, in accordance with someembodiments, to have one or more flowing gas curtains 180 flowing alonginterior surface(s) of window assembly 140. Each of these elements isdiscussed in turn below.

Window assembly 140 may include one or more optical windows. Thequantity and arrangement of optical windows, as well as the geometry anddimensions of each such optical window, may be customized, as desiredfor a given target application or end-use. As can be seen from FIG. 1 ,for example, window assembly 140 may include two optical windows—aforward end window 142 (generally closer to output coupler 120) and arearward end window 144 (generally closer to mirror 110). It should benoted, however, that the present disclosure is not intended to be solimited, as window assembly 140 may include a lesser quantity (e.g.,only one, such that mirror 110 is included within the volume of theflowing gases) or greater quantity (e.g., 3, 4, 5, 6, 7, 8, or more) ofoptical windows, in accordance with other embodiments. For example, ascan be seen from FIG. 11 (discussed below), for example, window assembly140 may include four optical windows—windows 142, 144 (discussed above),a first side window 146, and a second side window 148.

Additionally, the material composition, optical transmissioncharacteristics, and refraction of a given optical window 142, 144, 146,148 (or window assembly 140 more generally) may be customized, asdesired for a given target application or end-use, and generally maydepend on performance characteristics and requirements such asresilience to degradation, absorption of energy from pump beam 152 andoutput beam 10, and dimensional changes associated with energyabsorption, among others. In some embodiments, a given optical windowmay be constructed from fused silica or sapphire, for example. In someembodiments, a given optical window may be (A) coated with one or morecoating layers, such as a high-transmission coating or ahigh-reflectivity coating and/or (B) etched or embossed with ananotextured surface. In accordance with some embodiments, one or morewindows may be customized or contoured to provide (A) opticalrefraction, such as spherical or cylindrical lensing and/or (B)deflection (as through a prism), either of which may be segmented tovarious regions of the window or encompassing the whole window. Othersuitable configurations for window assembly 140, in part or in whole,will depend on a given target application or end-use and will beapparent in light of this disclosure.

As previously noted, flowing lasing gas 170 may be provided in lasingamplifier 130. More specifically, a gaseous amplifier gain medium may beutilized as flowing lasing gas 170, in accordance with some embodiments.The chemical composition, pressure, and vapor concentration of flowinglasing gas 170 may be customized, as desired for a given targetapplication or end-use. In accordance with some embodiments, flowinglasing gas 170 may be (or otherwise may include) any one (orcombination) of helium-4, helium-3, a hydrocarbon, and a fluorocarbon,to name a few options. In accordance with some embodiments, flowinglasing gas 170 may be substantially free of complex molecules (e.g.,such as hydrocarbons or fluorocarbons), relying on, for example, heliumas a quenching agent. In accordance with some other embodiments, one ormore complex molecules may be included as quenching agent(s). In atleast some hydrocarbon-free cases, the gas pressure may be maintained,for example, in the range of about 300-20,000 torr (e.g., about500-10,000 torr or any other sub-range in the range of about 300-20,000torr). In at least some cases that incorporate a quenching agent, thegas pressure may be maintained, for example, in the range of about50-1,500 torr (e.g., about 200-800 torr or any other sub-range in therange of about 50-1,500 torr). In accordance with some embodiments,flowing lasing gas 170 may include the vapor of one or more alkalimetals, such as rubidium (Rb), cesium (Cs), and/or potassium (K), toname a few. In accordance with some embodiments, flowing lasing gas 170may have an alkali metal vapor concentration in the range of about5×10¹¹ to 5×10¹⁴ atoms/cm³ (e.g., about 5×10¹¹ to 5×10¹² atoms/cm³,about 5×10¹² to 5×10¹³ atom s/cm³, about 5×10¹³ to 5×10¹⁴ atoms/cm³, orany other sub-range in the range of about 5×10¹¹ to 5×10¹¹ atom s/cm³).As will be appreciated in light of this disclosure, scenarios with lowergas pressure and/or higher output power generally may operate with loweralkali density, whereas others with higher pressure and/or lower outputpower (e.g., some cases involving helium as a quenching agent) mayoperate with higher alkali density, in accordance with some embodiments.

Additionally, the flow rate and flow direction of flowing lasing gas 170may be customized, as desired for a given target application or end-use.In accordance with some embodiments, flowing lasing gas 170 may have aflow rate through window assembly 140 (or lasing amplifier 130 moregenerally) in the range of about 1-100 m/s (e.g., about 10-25 m/s, about25-50 m/s, or any other sub-range in the range of about 1-10 m/s).Flowing lasing gas 170 may flow generally upward (e.g., generallyagainst the direction of gravity), generally downward (e.g., generallyin the direction of gravity), or transversely in any direction relativeto gravity. Other suitable characteristics for flowing lasing gas 170will depend on a given target application or end-use and will beapparent in light of this disclosure.

Also, as previously noted, one or more flowing gas curtains 180 may beprovided along interior surface(s) of window assembly 140. For example,in accordance with some embodiments, a single flowing gas curtain 180may be provided. In accordance with some other embodiments, an innerflowing gas curtain 180 a and an outer flowing gas curtain 180 b may beprovided. A given flowing gas curtain 180 may include a flow of one ormore gas(es) that do not include a substantial concentration of alkalivapor and may be provided over a given optical window through which (A)a given pump beam 152 and/or (B) output beam 10 passes in operation ofsystem 1000 a, in accordance with some embodiments.

The chemical composition and concentration of a given flowing gascurtain 180 may be customized, as desired for a given target applicationor end-use. In accordance with some embodiments, flowing gas curtain(s)180 a, 180 b may be of the same composition and pressure as flowinglasing gas 170 but be substantially depleted of alkali vapor, such thatflowing gas curtain(s) 180 a, 180 b may have a concentration of alkalivapor which is reduced by a factor in the range of about 3-500 (e.g.,about 5-50, about 10-20, or any other sub-range in the range of about3-500). Because there may be some mixing of gas(es) between the separateflow channels allowing some concentration to pass from the channel withflowing lasing gas 170 into the channel with the flowing gas curtain(s)180 a, 180 b, one or more additional flowing gas curtains 180 optionallymay be provided to achieve further reduction in the alkaliconcentration, in accordance with some embodiments.

Additionally, the flow velocity of a given flowing gas curtain 180 maybe customized, as desired for a given target application or end-use. Inaccordance with some embodiments, a given flowing gas curtain 180 mayhave a flow velocity along a given window of window assembly 140 (orlasing amplifier 130 more generally) that approximates the velocity offlowing lasing gas 170. In some embodiments, a given flowing gas curtain180 may have a velocity that differs from that of flowing lasing gas170, for example, by flowing in generally the same direction at a speedthat differs from that of flowing lasing gas 170 by about 0.1-30% (e.g.,about 0.1-10%, about 10-30%, or any other sub-range in the range ofabout 0.1-30%). In some cases, the difference may be a reduction of theflow speed of flowing gas curtain 180 by about 10%, for instance, tominimize (or otherwise reduce) any eddy currents.

Also, the temperature of a given flowing gas curtain 180 may becustomized, as desired for a given target application or end-use. Inaccordance with some embodiments, a given flowing gas curtain 180 mayhave a temperature that is less than the temperature of flowing lasinggas 170 by about 10-60° C. (e.g., about 10-20° C., about 20-30° C.,about 30-60° C., or any other sub-range in the range of about 10-60°C.). By maintaining a lower temperature, the equilibrium concentrationof alkali vapor in flowing gas curtain 180 may be reduced from that offlowing lasing gas 170. The temperature difference between flowinglasing gas 170 and an inner flowing gas curtain 180 a, for example, maybe limited because material surface(s) between the flow of flowinglasing gas 170 and any inner flowing gas curtain 180 a may reach anequilibrium temperature that is below the condensation temperature ofthe alkali in flowing lasing gas 170, thereby altering the properties offlowing lasing gas 170. Adding a second, outer flowing gas curtain 180 bmay relax this concern, as outer flowing gas curtain 180 b may bemaintained at a temperature that is much lower than either that offlowing lasing gas 170 or inner flowing gas curtain 180 a, substantiallyreducing the alkali concentration adjacent to a given window withoutaltering the properties of flowing lasing gas 170. Other suitablecharacteristics for flowing gas curtain(s) 180 will depend on a giventarget application or end-use and will be apparent in light of thisdisclosure.

The overall configuration of lasing amplifier 130 and arrangement offlowing gas curtain(s) 180 and flowing lasing gas 170 with respect towindow assembly 140 may be customized, as desired for a given targetapplication or end-use. In so doing, the bounds of flowing lasing gas170 and flowing gas curtain(s) 180 may be defined, at least in part. Forexample, consider FIG. 5 , which illustrates a partial view of system1000 a of FIG. 1 , in accordance with an embodiment of the presentdisclosure. As can be seen here, forward end window 142 and rearward endwindow 144 may be of substantially rectangular (e.g., square) geometryand arranged substantially parallel to one another. Flowing lasing gas170 may flow through lasing amplifier 130 between windows 142, 144. Aflowing gas curtain 180 may be provided between the flow of flowinglasing gas 170 and forward end window 142. Similarly, a flowing gascurtain 180 may be provided between the flow of flowing lasing gas 170and rearward end window 144. In at least some cases including both aninner flowing gas curtain 180 a and an outer flowing gas curtain 180 b,inner flowing gas curtain 180 a may flow between the flow of flowinglasing gas 170 and outer flowing gas curtain 180 b, while outer flowinggas curtain 180 b may flow between inner flowing gas curtain 180 a andthe adjacent window surface. In the example configuration of FIG. 5 ,window assembly 140, flowing gas curtains 180 (e.g., inner flowing gascurtain 180 a and outer flowing gas curtain 180 b), and the lasingvolume of flowing lasing gas 170 may exhibit a generally cubic shape. Itshould be noted, however, that the present disclosure is not intended tobe so limited, as in a more general sense, and in accordance with someother embodiments, a rectangular box shape or other parallelepiped shapemay be provided.

In some other embodiments, forward end window 142 and rearward endwindow 144 may be of substantially octagonal geometry and arrangedsubstantially parallel to one another. Flowing lasing gas 170 may flowthrough lasing amplifier 130 between windows 142, 144. A flowing gascurtain 180 may be provided over the interior of forward end window 142and rearward end window 144. In these example embodiments, windowassembly 140, flowing gas curtain(s) 180, and the lasing volume offlowing lasing gas 170 may exhibit a generally right octagonal prismshape. It should be noted, however, that the present disclosure is notintended to be so limited, as in a more general sense, and in accordancewith some other embodiments, a right hexagonal prism shape, a rightdecahedral prism shape, or other polyhedral prism shape may be provided.Note that, for unstable resonators 100 with negative magnification, theillumination pattern is inverted with each pass, so that the goal ofproviding edge surfaces that are congruent for pump beam(s) 152 andoutput beam(s) 10 may be achieved with a prism shape, for example, onlyif it has an even number of sides. For unstable resonators 100 withpositive magnification, the shape may not be so limited.

In some other embodiments, forward end window 142 and rearward endwindow 144 may be of substantially circular geometry and arrangedsubstantially parallel to one another. Flowing lasing gas 170 may flowthrough lasing amplifier 130 between windows 142, 144. A flowing gascurtain 180 may be provided between flowing lasing gas 170 and theinterior surface of forward end window 142 and/or rearward end window144. In these example embodiments, window assembly 140, flowing gascurtain(s) 180, and the lasing volume of flowing lasing gas 170 mayexhibit a generally right circular cylinder shape. It should be noted,however, that the present disclosure is not intended to be so limited,as in a more general sense, and in accordance with some otherembodiments, a right elliptical prism shape or other closed-curve prismshape may be provided.

As previously noted, system 1000 a may include one or more pump beamsources 150 configured to provide optical pumping for system 1000 a bydelivering one or more pump beams 152 to flowing lasing gas 170 inlasing amplifier 130. In accordance with some embodiments, a given pumpbeam source 150 may be configured to provide pump light which is highlycollimated along one axis (e.g., the fast axis) but divergent alonganother axis (e.g., the slow axis). As will be appreciated in light ofthis disclosure, the optical pumping wavelength(s) and spectrallinewidth(s), as well as the beam geometry, of the pump light may becustomized, as desired for a given target application or end-use. Aswill be further appreciated, in some cases, the pump beam 152 intensityemanating from a given pump beam source 150, on its own, may not besufficient for optimally pumping system 1000 a. Thus, in accordance withsome embodiments, a given pump beams 152 from multiple pump beam sources150 may be merged with (e.g., aligned along an adjacent trajectory) oroverlapped with one another.

The overall three-dimensional profile of pump beam 152, as well as itsaverage intensity, spatial illumination pattern, and divergences, may becustomized by placement of pump source 150 components together with oneor more beam-shaping optics 190 (e.g., refractive and/or reflectiveelements) along the optical path that modify the envelope of pump beam152 as it propagates from pump source 150 to the region of flowinglasing gas 170. For example, consider FIG. 6 , which illustrates anexample arrangement of pump beam source(s) 150 and beam-shaping optics190, in accordance with an embodiment of the present disclosure.Beam-shaping optics 190 may be configured, in accordance with someembodiments, to customize the profile of pump beam(s) 152 impinging onflowing lasing gas 170. As can be seen, pump beam source 150 may includea stack of laser diode array bars with a slow-axis dimension and afast-axis dimension. Due to the large divergence of pump beam 152 in theslow-axis direction, beam-shaping optics 190 (e.g., such as cylindricallenses 191, 192, 196, 197 and/or curved mirrors) configured, inaccordance with some embodiments, to magnify pump beam 152 along theslow-axis dimension may provide a divergence reduction, resulting inslow-axis divergence that more closely matches that of the fast axis,allowing greater collimation as pump beam 152 propagates a greater depththrough flowing lasing gas 170. Due to the low divergence of the fastaxis, beam-shaping optic(s) (e.g., such as cylindrical lenses 191, 192,196, 197 and/or curved mirrors) that serve to de-magnify (e.g.,concentrate) pump beam 152 along this direction generally may provide adivergence that more closely matches that of the slow axis. As will beappreciated in light of this disclosure, although this constitutes anincrease in the fast-axis divergence, it generally will not become thelimiting factor in the goal of aligning with or defining amplifiersurfaces that are shared with output beam(s) 10.

For some embodiments, a striped illumination pattern (attributable tothe alternation of diode array sources and dark regions due to theirheatsinks) may be present in flowing lasing gas 170. To eliminate (orotherwise reduce) this non-uniformity, a diffuser 199 may be added tothe optical arrangement to address (e.g., smear out) these variations,in accordance with some embodiments. In some cases, diffuser 199 may be,for example, a small-angled, engineered diffuser.

For some embodiments, achieving a three-dimensional profile whoselargest divergence (e.g., that of the slow axis) is minimized may beaided by incorporating a pump beam source 150 that has a large mismatchin its height-to-width ratio (e.g., with its large dimension along thefast axis (many bars aligned in one or more stacks) and its smalldimension along the slow axis (few bars or a single bar in width). Insome embodiments, the physical size of pump beam source 150 along thefast-axis direction may exceed the width of pump beam source 150 alongthe slow-axis direction, for instance, by a factor in the range of twoto twenty.

In some cases, the competing desires for de-magnifying (e.g.,concentrating) the illumination along the fast axis while still fillingthe desired illumination pattern may require a pump beam source 150whose size along the fast-axis direction (e.g., the number of bars inthe stack) exceeds recommended limits in the manufacturing process,exceeds space available along a single direction in system 1000 a, orcauses optical elements to become large. Thus, and in accordance withsome embodiments, one or more beam-combining elements may be employed.For instance, consider FIG. 7 , which illustrates an example arrangementof pump beam source(s) 150 and beam-combining optic(s) 198, inaccordance with an embodiment of the present disclosure. In some suchcases, pump beam source 150 may be segmented into a quantity ofcontributing pump beam source 150 elements, each with its angled faceton beam-combining optic(s) 198, so that the desired but unattainableheight is equal to the sum of the stack heights. In some embodiments,each pump beam source 150 may have its own transport optics and its ownregion of flowing lasing gas 170 to which its pump beam 152 illuminationis dedicated. In some such embodiments, pump beams 152 may be formedseparately but directed along an appropriate path so that theilluminated region from one contribution is made to be adjacent to thatof a neighboring contribution. As will be apparent in light of thisdisclosure, the quantity of pump beam sources 150 that may be combinedby beam-combining optic(s) 198 may be customized, as desired for a giventarget application or end-use. For instance, in some cases, two to fifty(or more) may be so combined.

In some cases, the length of the optical transport path may exceed thedesired dimension, due to one or more factors (e.g., the opticalarrangement required for magnifying the slow axis, for de-magnifying inthe fast axis, for minimizing the angle of incidence into alongitudinally pumped amplifier, etc.). In such cases, the optical pathmay be folded by reflecting the path using a turning mirror, inaccordance with some embodiments. In some instances, it may be desirableto have a portion of pump beam 152 encounter some optical element(s)while another portion thereof encounters different optical element(s).In some instances, one portion of pump beam 152 may be folded in amanner that differs from another portion. In some instances, there maybe pump beam sources 150 emanating from different path(s) that are thenused in combination to illuminate a region of flowing lasing gas 170. Inthese cases, pump beams 152 may be combined, for example, on amultifaceted mirror assembly, in accordance with some embodiments.

In some embodiments, pump beam 152 may illuminate flowing lasing gas 170longitudinally (e.g., through one or more windows that are also sharedby output beam 10). For such embodiments, it may be desirable toilluminate flowing lasing gas 170 via one or more pump beams 152oriented at an angle relative to output beam 10. If this angle can bechosen to be small and the divergence can be minimized, then the depthof the illuminated region of flowing lasing gas 170 can be greater.Furthermore, if the angle between the optical axis of pump beam 152 andoutput beam 10 is also chosen to lie along the slow axis of pump beam152, then the depth of the illuminated region of flowing lasing gas 170will be determined by the greater of these, and the fast axis of thepump array can be used to delineate a boundary that is shared by pumpbeam 152 and output beam 10. In some embodiments, the surface of theregion of flowing lasing gas 170 defined by the edge of fast-axisillumination is substantially perpendicular to the flow of flowinglasing gas 170, at the inlet of flowing lasing gas 170 into theamplifier region, and at the exit of flowing lasing gas 170 leaving theamplifier region. Then, assuming a rectilinear amplifier region, theedge of the illuminated region of flowing lasing gas 170 along the slowaxis will follow flow streamlines.

In some embodiments, the angle of pump beam 152 entering flowing lasinggas 170 along the slow axis, together with the divergence along the slowaxis, may be insufficient to provide a well-defined edge surfacethroughout the amplifier volume. In these instances, the parameters ofthe slow-axis afocal telescope may be chosen to maximize the overlapbetween the volume of flowing lasing gas 170 illuminated by pump beam152 and that illuminated by output beam 10. This may be accomplished,for example, by selecting a width of pump beam 152 at the focus and adepth into flowing lasing gas 170 where that focus is positioned.Furthermore, to maximize the illumination at some depth into flowinglasing gas 170 of an off-axis pump beam 152 with a significantdivergence, it may be useful to introduce a flowing side curtain toallow pump beam 152 transport to the region of flowing lasing gas 170without exciting portions of flowing lasing gas 170 that are notilluminated by output beam 10. For example, consider FIG. 8 , whichillustrates an example longitudinal pumping arrangement, in accordancewith an embodiment of the present disclosure. As can be seen here, pumpbeam source(s) 150 may impinge at an angle to illuminate flowing lasinggas 170. In some cases, as in FIG. 8 , the focus of the slow-axis afocaltelescope may lie at a depth roughly halfway within the amplifiervolume, with a width chosen as the width of output beam 10 (which thenbecomes the width of the amplifier). Tracing the angled rays of pumpbeam 152 back to the entrance window(s) 142 and/or 144, it can beappreciated that some rays may pass through a side region of flowing gascurtain 180, entering flowing lasing gas 170 through the side ratherthan the front. These rays may contribute to forming a slow-axis focusat some depth within the amplifier volume of flowing lasing gas 170.

As will be appreciated in light of this disclosure, the illuminationuniformity may be compromised in off-axis longitudinal pumping, mostnotably that two corners at the edge of pump beam 152 (or beyond itscoverage) may have lower illumination intensity (or none at all). Insome embodiments, flowing lasing gas 170 may be pumped from more thanone side (e.g., two sides) of output beam 10 along the slow-axisdirection, such that illumination from multiple pump beams 152 emanatingfrom these multiple sides may share the same edge at the input offlowing lasing gas 170 and at the exit of flowing lasing gas 170 definedby the edge of the fast-axis illumination. In some embodiments, flowinglasing gas 170 may be pumped from multiple sides (e.g., four sides) ofoutput beam 10, such that illumination from multiple pump beams 152emanating from two of these multiple sides may share the same edge atthe input of flowing lasing gas 170 and at the exit of flowing lasinggas 170 defined by the edge of the fast-axis illumination, and the otherpump beams 152 may illuminate the active region up to that edge, as nearas possible with the illumination along the direction of the slow-axisdivergence. In some embodiments, flowing lasing gas 170 may be pumpedalong paths emanating from these multiple sides of output beam 10through window 142 covering the amplifier end closest to output coupler120. In some embodiments, flowing lasing gas 170 may be pumped alongpaths whose central axis is angled with respect to output beam 10 frommultiple sides of output beam 10 through window 144 covering theamplifier end closest to high-reflectivity mirror 110.

In some embodiments, flowing lasing gas 170 may be pumped through bothend window 142 (closest to output coupler 120) and end window 144(closest to high-reflectivity mirror 110). As will be appreciated inlight of this disclosure, it may be desirable to avoid alignment of twopowerful pump beams sources 150 pointed directly at one another. In suchcases, a perfect alignment of the fast-axis light from the two ends thatdefine common edge surfaces that are shared by pump beam 152 and outputbeam 10 may cause the optical axes of the two opposing pump beams 152 tobe shared, such that any pump light transmitted through flowing lasinggas 170 originating on one side may propagate into the laser on theother side. For these instances, an alternate alignment that providesfor a small angle, for example, in the range of about 1-5° (e.g., about2-4° or any other sub-range in the range of about 1-5°) between theoptical plane of the fast-axis light entering from one end and thefast-axis light entering from the opposite end optionally may beemployed, in accordance with some embodiments. For example, considerFIG. 9 , which illustrates an example longitudinal pumping arrangement,in accordance with an embodiment of the present disclosure. As can beseen, this arrangement includes four pump beam sources 150 contributingto longitudinal pumping of a flowing lasing gas 170 with flowing gascurtain(s) 180 at both ends and on both sides, in accordance with someembodiments. After passing through flowing lasing gas 170, each of thesetransmitted beams 152 may follow a different optical path that isdistinct from the incoming beam 152. It, therefore, can be made topropagate through the final fast-axis focusing element on the opposingside and arrive at the fast-axis focal plane, albeit at a differentlocation in that focal plane due to the different angle in the flowinglasing gas 170. Where the transmitted beam 152 comes to a focus at aunique region of the focal plane in the opposing laser's optical path,it optionally may be deflected along a unique path for purposes ofcharacterization, quantification, and/or absorption. In some such cases,the edge surface may become more complex, requiring additional care inassuring that unstable resonator 100 illuminates all pumped regions withoutput beam 10.

As previously noted, system 1000 a also may include one or more pumpbeam edge-defining elements 160. Pump beam edge-defining element(s) 160may be configured, in accordance with some embodiments, to help create(e.g., define and/or refine) a stronger edge for incident pump beam 152light. In accordance with some embodiments, pump beam edge-definingelement(s) 160 may include one or more mirrors, one or more opticalelements, and/or one or more light-absorbing masks.

In some cases, the divergence of the slow axis may cause an illuminationpattern which decreases with distance away from the fully illuminatedregion, such that the illumination intensity transitions past a levelthat may not be optimal for creating gain in this region of flowinglasing gas 170. In those instances, the design of the illuminationpattern may face a choice of alternatives. That is, if the illuminationpattern of unstable resonator 100 is chosen to not include the regionthat is insufficiently pumped, then that region may contribute tospontaneous emission near the edge of flowing lasing gas 170, causinginefficiencies in the adequately pumped regions due to amplifiedspontaneous emission (ASE). If instead the illumination pattern ofunstable resonator 100 does include the region that is insufficientlypumped, then that illumination from the magnified pump beam 152 inunstable resonator 100 may not be optimally used. Thus, where pump beam152 light can be deflected and employed for useful gain, one or moremirrors may be placed to define the edge of the illumination pattern atthe location where pump beam 152 enters flowing lasing gas 170 to make adefining cut in the tail of the slow-axis light, deflecting raysimpinging toward the low-illumination region back into thehigh-intensity region, in accordance with some embodiments. In somecases where slow-axis illumination extending outside the adequatelyilluminated region cannot be deflected and usefully used for gain, itmay be simply absorbed on one or more light-absorbing masks outside theflowing lasing gas 170 region, so that its power does not contribute tointernal heating and inefficiencies, in accordance with someembodiments. In either of these example scenarios, the definition of thepump beam 152 edge(s) may be improved, as the width of the edge in theamplifier region then will be defined by the width of the slow-axisdivergence projected the distance into flowing lasing gas 170, growingby the product of the divergence times the distance as it propagatesmore deeply into flowing lasing gas 170, in accordance with someembodiments.

The quantity and arrangement of mirrors, optical elements, and/or masksof pump beam edge-defining element(s) 160 may be customized, as desiredfor a given target application or end-use. In some embodiments, pumpbeam edge-defining element(s) 160 may include two mirrors arranged todefine two edges of the slow-axis illumination provided by pump beam152. In some embodiments, pump beam edge-defining element(s) 160 mayinclude four mirrors arranged in a box-like shape to define four edgesof the illumination provided by pump beam 152. It should be noted,however, that the present disclosure is not intended to be so limited,as in accordance with other embodiments, pump beam edge-definingelement(s) 160 may include fewer (e.g., 1, 2, or 3) or more (e.g., 5, 6,7, 8, or more) mirrors, optical elements, and/or light-absorbing masks,as desired.

In accordance with some embodiments, pump beam edge-defining element(s)160 may include a mirror assembly disposed near an intersection of pumpbeam 152 and the optical pathway of unstable resonator 100 andconfigured to have pump beam 152 incident therewith. In some cases, themirror assembly may be configured to reflect at least a portion of pumpbeam 152 so as to define the edge of pump light incident therewith.

In accordance with some embodiments, pump beam edge-defining element(s)160 may include an assembly of optical elements (e.g., lenses, mirrors,etc.) disposed outside of the optical pathway of unstable resonator 100and configured to have pump beam 152 pass therethrough. In someinstances, the assembly of optical elements may be configured torefractively optically transport and/or reflectively optically transportat least a portion of pump beam 152 so as to define the edge of pumplight incident therewith. In some cases, the assembly of opticalelements may be configured to form an image of at least a portion ofpump beam 152 so as to define the edge of pump light incident therewith.

In accordance with some embodiments, pump beam 152 may enter the regionof flowing lasing gas 170 axially, along the same optical path as outputbeam 10, by being deflected into flowing lasing gas 170 by an elementthat is transparent to output beam 10. In some cases, that element mayreflect pump beam 152 and transmit output beam 10 due to a difference in(A) the direction of their linear polarization and/or (B) wavelength. Bythese and other methods, pump beam 152 and output beam 10 may achievegreater alignment for the goal of sharing edge surfaces that define theboundaries of the amplifier volume, in accordance with some embodiments.

As previously noted, system 1000 a may be configured, in accordance withsome embodiments, for longitudinal pumping of flowing lasing gas 170 inlasing amplifier 130. In such cases, pump beam(s) 152 may enter pumpbeam edge-defining element(s) 160, being incident with one or moreconstituent mirrors, optical elements, and/or masks thereof, andsubsequently enter lasing amplifier 130 through forward end window 142(of window assembly 140) for delivery to flowing lasing gas 170 (inlasing amplifier 130). Output beam 10 may enter/exit lasing amplifier130 through forward end window 142 and rearward end window 144 (ofwindow assembly 140). Output beam 10 may have an intermediate focuspoint 12. The portion of output beam 10 passing beyond the outer boundsof output coupler 120 may be utilized downstream of system 1000 a. Also,downstream of output coupler 120, output beam 10 may include an interiordark region 14 resulting from upstream masking by output coupler 120.

As will be appreciated in light of this disclosure, an arrangement ofpump beam sources 150, pump beam optical transport elements andapertures (e.g., beam-shaping optics 190, pump beam edge-definingelements 160), and flowing gas curtains 180 that provides definition ofthe edges of the amplifier region, together with the configuration of anunstable resonator 100 (e.g., a confocal unstable resonator) thatproduces an output beam 10 with the same edge surfaces, may allow foramplifier regions with a greater dimensional aspect ratio (e.g., theratio of the length along output beam 10 to the transverse size). Insome cases, the length may be substantially equal to the transversedimension (e.g., an aspect ratio of unity). In some other cases, theaspect ratio may exceed unity, in some instances significantly.

Transversely Pumped System Architecture and Operation

FIG. 10 illustrates a gaseous laser system 1000 b configured fortransverse pumping in accordance with another embodiment of the presentdisclosure. As can be seen, system 1000 b may be configured much likesystem 1000 a discussed above. As will be appreciated in light of thisdisclosure, the description provided above with respect to the variousconstituent elements and characteristics of system 1000 a—for instance,unstable resonator 100, lasing amplifier 130, flowing lasing gas 170,flowing gas curtains 180, pump beam sources 150, output beam 10,beam-shaping optic(s) 190 (e.g., lenses, folding mirrors, apertures,diffusers, beam-combining mirrors, etc.), pump beam edge-definingelement(s) 160 (e.g., mirrors, optical elements, masks, etc.), etc.— mayapply equally here, in part or in whole, in the context of system 1000b, in accordance with some embodiments. As can be seen further, system1000 b may include one or more pump beam sources 150 for transversepumping of lasing amplifier 130 via one or more pump beams 152.Additionally, system 1000 b may include beam-shaping optics 190 (e.g.,beam-combining optic 198, diffuser 199) for the fast and slow axes, aswell as have fast-axis and slow-axis focus points 193.

As with system 1000 a described above, here in system 1000 b, lasingamplifier 130 may include a window assembly 140 in which a flowinglasing gas 170 may be provided. Lasing amplifier 130 further may beconfigured, in accordance with some embodiments, to have one or moreflowing gas curtains 180 (e.g., inner flowing gas curtain 180 a and/orouter flowing gas curtain 180 b) flowing along surface(s) interior towindow assembly 140.

In accordance with some embodiments, window assembly 140 of system 1000b may include four optical windows: (1) a forward end window 142(generally closer to output coupler 120); (2) a rearward end window 144(generally closer to high-reflectivity mirror 110); (3) a first sidewindow 146; and (4) a second side window 148 (situated substantiallyopposite first side window 146). It should be noted, however, that thepresent disclosure is not intended to be so limited, as in accordancewith other embodiments, window assembly 140 may include fewer (e.g., 1,2, or 3) or more (e.g., 5, 6, 7, 8, or more) optical windows, asdesired.

Also, as previously noted, a flowing lasing gas 170 may be provided inlasing amplifier 130. More specifically, a gas mixture including atleast some concentration of a lasing component (e.g., a gaseousamplifier) may be utilized as flowing lasing gas 170, in accordance withsome embodiments.

Furthermore, as previously noted, one or more flowing gas curtains 180may be provided along interior surface(s) of window assembly 140. Morespecifically, a flow of a gas depleted or devoid of the lasing component(and, therefore, substantially transparent to pump beam 152 and outputbeam 10) may be provided to flow over a given optical window throughwhich (i) pump beam 152 and/or (ii) output beam 10 passes in operationof system 1000 b, in accordance with some embodiments. In some cases,flowing gas curtain 180 may include the same component gases as flowinglasing gas 170, with the exception of being depleted or devoid of thelasing component. In some cases, the depletion of the concentration ofthe lasing component in the gas of flowing gas curtain 180 may beaccomplished by maintaining that gas at a temperature which is lowerthan that of flowing lasing gas 170. In some cases, flowing gas curtain180 may be further subdivided so that an inner flowing gas curtain 180 ais depleted of the lasing component, while an outer flowing gas curtain180 b is further depleted of the lasing component. In some cases, innerflowing gas curtain 180 a and outer flowing gas curtain 180 b may bemaintained at different temperatures. In those cases, inner flowing gascurtain 180 a may be maintained at a temperature lower than flowinglasing gas 170 so that the concentration of the lasing component isreduced, but not so low a temperature that flow boundary materials thatare in contact with both the lasing component of flowing lasing gas 170and the gas of inner flowing gas curtain 180 a become sufficientlyreduced in temperature as to cause condensation of the lasing componentor otherwise alter its concentration. In those cases, outer flowing gascurtain 180 b, flowing adjacent to the inner surface of the window, maybe maintained at a temperature much lower than that of inner flowing gascurtain 180 a or flowing lasing gas 170, so that it can be maintainedessentially devoid of the lasing component.

As with system 1000 a described above, here in system 1000 b, theoverall configuration of lasing amplifier 130 and arrangement of flowinggas curtain(s) 180 and flowing lasing gas 170 with respect to windowassembly 140 may be customized, as desired for a given targetapplication or end-use. For example, consider FIG. 11 , whichillustrates a partial view of system 1000 b of FIG. 10 , in accordancewith an embodiment of the present disclosure. As can be seen here,forward end window 142 and rearward end window 144 may be ofsubstantially rectangular (e.g., rectangular or square) geometry andarranged substantially parallel to one another. As can be seen further,first side window 146 and second side window 148 may be of substantiallyrectangular (e.g., rectangular or square) geometry and arrangedsubstantially parallel to one another. Thus, windows 142, 144, 146, 148may be arranged to form a four-sided, open-ended, box-like shape, asgenerally shown. Flowing lasing gas 170 may flow through lasingamplifier 130 between windows 142, 144, 146, 148.

Further regarding the example arrangement of FIG. 11 , flowing gascurtain(s) 180 may be provided to flow between flowing lasing gas 170and (optionally) any or all windows 142, 144, 146, 148. Optionally, aflowing gas curtain 180 between flowing lasing gas 170 and any/allwindows 142, 144, 146, 148 may be subdivided into an integer number ofsubregions, in accordance with some embodiments. For example, ifsubdivided into two subregions, one flow may be an inner flowing gascurtain 180 a adjacent to the flow of flowing lasing gas 170 and anotherflow may be an outer flowing gas curtain 180 b between that innerflowing gas curtain 180 a and the inside surface of a given window 142,144, 146, 148. In the example configuration of FIG. 11 , window assembly140, flowing gas curtains 180, and the lasing volume of flowing lasinggas 170 may exhibit a generally rectilinear shape, where the height andwidth that define the dimensions of output beam 10 are approximatelyequal and the length is generally greater than either. In cases wherethe height and width are equal, then the aspect ratio is defined as theratio of the length to the transverse dimension. It should be noted,however, that the present disclosure is not intended to be so limited,as in a more general sense, and in accordance with some otherembodiments, an asymmetrical beam shape may be desired, and therectangular box shape may have an aspect ratio that is greater than orless than unity.

As noted above, system 1000 b may include beam-shaping optic(s) 190. Inaccordance with some embodiments, beam-shaping optic(s) 190 may beconfigured to transport pump beam 152 from pump source 150 to flowinglasing gas 170 while altering the dimensions of the pump beam 152envelope as well as its divergence along the fast and slow axes. In somecases, beam-shaping optic(s) 190 may include one or more elementsarranged to de-magnify the fast-axis illumination and magnify theslow-axis illumination. In accordance with some embodiments,beam-shaping optic(s) 190 may be configured as an afocal telescope. Insome embodiments, beam-shaping optic(s) 190 may include cylindricallenses 191, 192, 196, 197 and/or curved mirrors. In some cases, anintermediate focus point 193 optionally may be included. In someembodiments, beam-shaping optic(s) 190 may include cylindrical lens(es)191, 192, 196, 197, providing an afocal telescope in either (or both)the fast and slow axes, optionally with (1) a focus of the fast-axisrays at a point 193 between the elements that focus along the fast-axisdimension and/or (2) a focus of the slow-axis rays at a point 193between the elements that focus along the slow-axis dimension. In someembodiments, beam-shaping optic(s) 190 may include one or more mirrorsconfigured to fold the optical path, thereby making it more compact. Insome embodiments, beam-shaping optic(s) 190 may include curvedmirror(s), providing focusing along one or more axes while also foldingthe optical path, thereby making it more compact.

As noted above, in some cases, several pump beam sources 150 (e.g.,several stacks of laser diode bars) may be utilized. In some instances,it may be desirable to combine pump beams 152 of several pump beamsources 150 so that they form a substantially continuous illumination offlowing lasing gas 170, as if they emanated from a continuous pump beamsource. Pump beam 152 combining may involve deflection of an entire pumpbeam 152 from one or more pump beam sources 150 by unique and differingangles so that the optical rays at the extreme edge of one pump beam 152are adjacent and in alignment (e.g., having path and trajectory thatchange smoothly and continuously in both position and angle) with theoptical rays at the adjacent extreme edge of the next pump beam 152. Inaccordance with some embodiments, this may be accomplished by using amultifaceted beam-combining mirror 198. In some embodiments, such mirror198 may be positioned before the final converging element ofbeam-shaping optics 190 (e.g., the fast-axis telescope) and may providedeflections in the fast-axis direction. In some embodiments, beamcombining may be accomplished using one or more prisms. In someembodiments, the prism(s) may be positioned to deflect in the slow-axisdirection and may be positioned close to pump beam source 150 justbefore the slow-axis divergence causes pump beams 152 from two adjacentpump beam sources 150 to overlap and (optionally) may provide acorrecting deflection at the image plane just before side window 146 ofwindow assembly 140. It should be noted, however, that the presentdisclosure is not intended to be so limited, as in accordance with otherembodiments, beam-shaping optic(s) 190 may include fewer (e.g., one) ormore (e.g., 3, 4, 5, 6, 7, 8, or more) lenses, mirrors, and/or prisms,as desired.

Furthermore, as noted above, when pump beams 152 are configured to pumpa volume from opposite sides while sharing common surfaces at the flowentrance and exit, the transmitted pump beams 152 may enter the opticalpath of the laser on the opposing side. By canting pump beams 152 fromthe two sides at a small relative angle (e.g., about 5° or less) whilestill maintaining those common surfaces as much as practical, thetransmitted pump beam 152 may be made to pass through the fast-axisfocus 193 at a sufficiently distinct location so that it can bedeflected.

The geometry and dimensions of a given lens of beam-shaping optic(s) 190may be customized, as desired for a given target application or end-use.In accordance with some embodiments, a given amplifier volume, if chosento be rectilinear and symmetric as to height and width, may have anaspect ratio (e.g., the ratio of the length to the transverse dimension)ranging from about 0.3-50 (e.g., about 2-8 or any other sub-range in therange of about 0.3-50).

As will be appreciated in light of this disclosure, although it may bedesirable for diode laser stacks to have a height comprised of manybars, there are challenges to producing stacks with height greater than20-50 bars (although some provide up to 100 or 150 bars). With the aboveprovisions for combining pump beams 152 from multiple pump beam sources150 along their fast axis using beam-combining mirror(s) 198, pump beamsource 150 arrays easily can incorporate, for instance, eight stacks perside, with clear methods for reaching 32 or even 64 stacks combinedalong the fast axis, per side widow pump. Furthermore, pump beams 152from multiple pump beam sources 150 may be combined along their slowaxis, easily incorporating, for instance, eight stacks along the beamline. If a design is willing to forgo the divergence-reduction benefitsof beam magnifying along the slow-axis (e.g., reducing the divergence inthe amplifier so that the end surface is well-defined), then the slowaxis may be illuminated simply by the overlap of the divergent beamsfrom many pump beam sources 150, in accordance with some embodiments. Inthis case, combining two, ten, or even fifty or more stacks along theslow axis may become relatively straightforward, as the illuminationpattern may be terminated at the ends (both the end nearest outputcoupler 120 and the end nearest high-reflectivity mirror 110) by a pumpregion-defining mirror, to deflect the slow-axis tail of pump beam 152back into the uniformly illuminated gain region.

As flowing lasing gas 170 may have a single chosen concentration, it maybe desirable, at least in some instances, to ensure that theillumination distribution of pump beam(s) 152 is as uniform as possible.However, the optical transport system described above (e.g.,beam-shaping optic(s) 190) may include one or more afocal telescopesalong one or more of the fast-axis and slow-axis directions, creating animage of pump beam source 150 (near the region of flowing lasing gas170) which has dark regions between bars and may have localized darkregions due to individual emitters that underperform. To address this, adiffuser 199 optionally may be incorporated into the optical transportsystem for pump beam 152, in accordance with some embodiments. In somecases, such diffuser 199 may be disposed, for example, near a waist ofpump beam 152.

It should be noted, however, that the characteristics of a givencomponent of beam-shaping optic(s) 190 are not intended to be solimited. For example, in some cases, stepped mirror(s) may be utilizedto eliminate dark spaces between bars, thereby increasing theillumination intensity without increasing the divergence, in accordancewith some embodiments. In some embodiments, pump beams 152 may beprepared from two pump beam sources 150 with polarizations perpendicularto one another and combined through an element that transmits onepolarization and reflects the other. In some embodiments, two pump beamsources 150 may be positioned so that their pump beams 152 are spatiallyoffset in the fast-axis direction by one-half-bar spacing and combinedusing a comb-like reflector, such that pump beams 152 from one stack arereflected on stripes of mirrors while pump beams 152 from the companionoffset stack are transmitted through the gaps between those reflectivestripes. Other suitable configurations for beam-shaping optic(s) 190will depend on a given target application or end-use and will beapparent in light of this disclosure.

Pump Beam Intensity Distributions

Returning to FIG. 12A (discussed above), at least one existing approachto producing a DPAL system seeks to confine pump power (100 kW) within aspatial distribution that resembles a Gaussian, having a width as narrowas possible, a central peak illumination as high as possible, and apoorly defined edge. Such a distribution may be accomplished by placingdiode stack pump sources close to the amplifier region so that theslow-axis divergence does not spread too much, choosing a stack heightalong the fast-axis that approximates the desired width, and positioningseveral stack sources around a quasi-spherical dome, all aimed at thecenter of the amplifier region. Presuming a FWHM (in both directions) of3.6 cm, the peak intensity might be very high (as high as 26 kW/cm²)with a portion of that power penetrating flowing lasing gas 170 andemerging out the other end underutilized. The full width at one-tenthmaximum (FWTM) would be 6.58 cm, providing an intensity of 2.6 kW/cm² ata radius of 3.29 cm, with intensity dropping rapidly with radius. Atmuch larger radii, the pump intensity would be insufficient to maintaina population inversion, leading to unity or negative gain. Furthermore,the pump illumination spatial profile forms a waist along the axis atsome depth within the amplifier region, with increased transversedimension near the front and back of the amplifier. It has been observedthat the threshold for DPAL lasing is typically on the order of 200W/cm² under the right conditions. Pump illuminations of 2.6 kW/cm² canachieve up to 70-85% efficiency (depending on the spectral linewidth ofthe pump source, the pressure of the gas medium, and other factors), butonly with optimally chosen alkali density. However, raising the alkalidensity above this level to absorb a significant fraction of the centralpeak intensity may cause the regions pumped at lower intensity to haveincomplete penetration of the pump illumination and, thus, may producenegative gain.

Contrary to FIG. 12A discussed above, FIGS. 12B-12E illustrate severalexample pump beam intensity distributions in accordance with someembodiments of the present disclosure. As can be seen from FIG. 12B, thepump beam intensity along the fast axis may be comprised of severalsegments, each from a different pump source and de-magnified (e.g.,concentrated), aimed such that their illumination patterns just touchbut do not overlap. Since they are comprised of the de-magnified imagesof the pump beam sources 150 which are themselves comprised ofilluminating bars with dark regions between them, a diffuser 199 placedin the path (optionally near the waist of pump beam 152) may be used tohomogenize pump beam 152 output thereby. The edge of the illuminationmay be defined by the diffused image of the final bar of the final stackin the array of pump beam source 150.

As can be seen from FIG. 12C, the pump beam intensity along the slowaxis also may be comprised of several segments, each from a differentpump beam source 150, and transported through one or more beam-shapingoptics 190 to illuminate the amplifier region of flowing lasing gas 170.In some embodiments, the beam-shaping optics 190 may include an afocaltelescope such that an image of the slow axis may be formed near theamplifier region. In some such embodiments, those afocal telescopes mayincorporate one or more beam deflectors, such as prisms, to allow theirillumination patterns to just touch but not overlap. The edge of theillumination may be formed by the edge of the stack and may divergethrough the amplifier region according to the (magnified) divergence ofthe slow axis. In some embodiments, the array of pump beam source 150may be required to illuminate an amplifier region that may be quitelong, especially in cases of transverse pumping.

As can be seen from FIG. 12D, the pump beam intensity along the slowaxis may be comprised of the overlapping beams projected directly fromthe pump sources to the illuminated region of flowing lasing gas 170,without slow-axis transport optics. In these cases, the edge of theillumination may not be well-defined but instead may be formed by theprojected slow-axis divergence. In these cases, as can be seen from FIG.12E, it may be beneficial to introduce mirrors at the edge of theslow-axis illumination to produce a well-defined edge and to relocatethe divergent pump light back into the illuminated region of flowinglasing gas 170. The arrangement of mirrors may be accomplished by one ormore mirrors approximately parallel to the path of the pump rays,deflecting them into the amplifier through small angle reflections, orby two or more mirrors approximately perpendicular to the path of therays, reflecting them back towards pump beam source 150, and thenreflecting again into the illuminated region of flowing lasing gas 170.

It should be noted, however, that these techniques are not intended tobe the only approach to accomplishing a well-defined edge of a pump beam152 that is shared by output beam 10. For example, as will be apparentin light of this disclosure, definition of the edge surfaces may beaccomplished using an engineered diffuser 199 to produce a pump beam 152with uniform intensity and a well-defined edge, in accordance with someembodiments.

Thus, as will be appreciated in light of this disclosure, the exampleexisting approach for longitudinal pumping discussed above in relationto FIG. 12A may be improved upon using techniques disclosed herein, inaccordance with some embodiments. For instance, distributing the 100 kWof pump power uniformly, in accordance with some embodiments, at 2.6kW/cm² may allow for uniformly illuminating a square region with 6.2 cmon a given side. Because the divergence of the pump beam can be reducedfrom as much as 45° to about 5° (e.g., the angle required between thetransport optics of the pump array and the beam path), the amplifierregion can be extended along the beam path from 2 cm to 20 cm, inaccordance with some embodiments. In accordance with some embodiments,the alkali density may be chosen to maximize the gain for thisillumination intensity and may be a much lower alkali density than inthe aforementioned existing approach. Moreover, greater length of theamplification region, lower peak pump intensity, lower peak beamintensity, and lower alkali density may produce lower levels ofparasitic physics processes, such as energy pooling, ionization, andamplified spontaneous emission (ASE), in accordance with someembodiments.

The foregoing description of example embodiments has been presented forthe purposes of illustration and description. It is not intended to beexhaustive or to limit the present disclosure to the precise formsdisclosed. Many modifications and variations are possible in light ofthis disclosure. It is intended that the scope of the present disclosurebe limited not by this detailed description. Future-filed applicationsclaiming priority to this application may claim the disclosed subjectmatter in a different manner and generally may include any set of one ormore limitations as variously disclosed or otherwise demonstratedherein.

What is claimed is:
 1. A gaseous laser system comprising: a pump beamsource configured to emit a pump beam having at least one edge surface;and an unstable resonator configured to produce an output beam having atleast one edge surface defined by a drop in intensity that is moreabrupt than that of a Gaussian profile; wherein the gaseous laser systemis configured to have a gas mixture flowing therethrough, the gasmixture comprising a gas and an active lasing agent; and wherein aspatial volume defined by intersection of the pump beam, the flowing gasmixture, and the output beam forms a lasing amplifier, wherein at leasta portion of an outer boundary of the spatial volume of the lasingamplifier is defined by and shared with the at least one edge surface ofthe pump beam and the at least one edge surface of the output beam. 2.The gaseous laser system of claim 1, further comprising an edge-definingelement configured to define an edge of the pump beam, wherein theedge-defining element comprises at least one of a mirror, a lens, and amask disposed near an intersection of the pump beam and an opticalpathway of the unstable resonator and configured to have the pump beamincident therewith.
 3. The gaseous laser system of claim 2, wherein theat least one of a mirror, a lens, and a mask is configured to intersectwith at least a portion of the pump beam so as to define the edgethereof.
 4. The gaseous laser system of claim 1, further comprising anedge-defining element configured to define an edge of the pump beam,wherein the edge-defining element comprises an assembly of opticalelements disposed outside of an optical pathway of the unstableresonator and configured to have the pump beam pass therethrough.
 5. Thegaseous laser system of claim 4, wherein the assembly of opticalelements is configured to at least one of refractively opticallytransport and reflectively optically transport at least a portion of thepump beam so as to define the edge thereof.
 6. The gaseous laser systemof claim 4, wherein the assembly of optical elements is configured toform an image of at least a portion of the pump beam so as to define theedge thereof.
 7. The gaseous laser system of claim 1, further comprisingan optical window assembly through which the gas mixture flows inoperation of the gaseous laser system, wherein the gaseous laser systemis configured to have at least one flowing gas curtain pass over aninterior surface of the optical window assembly in a region throughwhich the pump beam passes in operation of the gaseous laser system. 8.The gaseous laser system of claim 7, wherein the at least one flowinggas curtain comprises an inactive gas.
 9. The gaseous laser system ofclaim 7, wherein the at least one flowing gas curtain is configured tohave the pump beam incident therewith so as to define an edge of thepump beam.
 10. The gaseous laser system of claim 1, wherein the gaseouslaser system is configured as a diode-pumped alkali laser (DPAL) and theactive lasing agent comprises a vapor of an alkali metal.
 11. Thegaseous laser system of claim 1, wherein the lasing amplifier is boundedwith a first edge surface on a first side thereof and a second edgesurface on an opposing second side thereof, the spatial volume residingbetween said first and second edge surfaces, wherein said first andsecond edge surfaces are formed by and co-located with the at least oneedge surface of the pump beam and the at least one edge surface of theoutput beam.
 12. The gaseous laser system of claim 1, wherein the lasingamplifier is bounded by at least one edge surface defined by an abrupttransition in concentration of the active lasing agent in the gasmixture.
 13. The gaseous laser system of claim 12, wherein the lasingamplifier is bounded by: at least two edge surfaces on opposites sideswhich are formed by and co-located with the at least one edge surfacedefined by the abrupt transition in concentration of the active lasingagent in the gas mixture; and at least two edge surfaces on oppositesides which are formed by and co-located with the at least one edgesurface of the pump beam and the at least one edge surface of the outputbeam.
 14. A method of operating a gaseous laser system, the methodcomprising: emitting a pump beam having at least one edge surface;producing an output beam having at least one edge surface defined by adrop in intensity that is more abrupt than that of a Gaussian profile;and providing a flowing gas mixture comprising a gas and an activelasing agent; wherein a spatial volume defined by intersection of thepump beam, the flowing gas mixture, and the output beam forms a lasingamplifier, wherein at least a portion of an outer boundary of thespatial volume of the lasing amplifier is defined by and shared with theat least one edge surface of the pump beam and the at least one edgesurface of the output beam.
 15. The method of claim 14, furthercomprising: defining an edge of the pump beam via at least one of areflection process, an image forming process, and a masking process. 16.The method of claim 14, further comprising: defining an edge of the pumpbeam via at least one of a refractive optical transport process and areflective optical transport process.
 17. The method of claim 16,wherein the at least one of the refractive optical transport and thereflective optical transport process comprises: focusing the pump beamthrough at least one lens before delivering the resultant pump beam tothe flowing gas mixture.
 18. The method of claim 14, further comprising:passing the pump beam through at least one flowing gas curtain providedadjacent to the flowing gas mixture.
 19. The method of claim 18, whereinthe at least one flowing gas curtain comprises an inactive gas.
 20. Themethod of claim 14, wherein the gaseous laser system is configured as adiode-pumped alkali laser (DPAL) and the active lasing agent comprises avapor of an alkali metal.
 21. A gaseous laser system comprising: a pumpbeam source configured to emit a pump beam having at least one edgesurface; and an unstable resonator configured to produce an output beamhaving at least one edge surface defined by a drop in intensity that ismore abrupt than that of a Gaussian profile; wherein the gaseous lasersystem is configured to have a gas mixture flowing therethrough, the gasmixture comprising a gas and an active lasing agent; and wherein theflowing gas mixture has at least one edge surface defined by an abrupttransition in concentration of the active lasing agent in the gasmixture, wherein said at least one edge surface is a shared edge surfaceshared by at least one of: the at least one edge surface of the pumpbeam; and the at least one edge surface of the output beam.
 22. Thegaseous laser system of claim 21, wherein: a spatial volume defined byintersection of the pump beam, the flowing gas mixture, and the outputbeam forms a lasing amplifier; and the lasing amplifier is bounded witha first edge surface on a first side thereof and a second edge surfaceon an opposing second side thereof, the spatial volume residing betweensaid first and second edge surfaces, wherein said first and second edgesurfaces are formed by and co-located with the at least one edge surfacedefined by the abrupt transition in concentration of the active lasingagent in the gas mixture and the at least one edge surface of the pumpbeam.
 23. The gaseous laser system of claim 21, wherein: a spatialvolume defined by intersection of the pump beam, the flowing gasmixture, and the output beam forms a lasing amplifier; and the lasingamplifier is bounded with a first edge surface on a first side thereofand a second edge surface on an opposing second side thereof, thespatial volume residing between said first and second edge surfaces,wherein said first and second edge surfaces are formed by and co-locatedwith the at least one edge surface defined by the abrupt transition inconcentration of the active lasing agent in the gas mixture and the atleast one edge surface of the output beam.
 24. The gaseous laser systemof claim 21, wherein: a spatial volume defined by intersection of thepump beam, the flowing gas mixture, and the output beam forms a lasingamplifier; and the lasing amplifier is substantially rectilinear ingeometry, being bounded with: two edge surfaces on opposite sides whichare formed by and co-located with the at least one edge surface definedby the abrupt transition in concentration of the active lasing agent inthe gas mixture and the at least one edge surface of the output beam;two edge surfaces on opposite sides which are formed by and co-locatedwith the at least one edge surface defined by the abrupt transition inconcentration of the active lasing agent in the gas mixture and the atleast one edge surface of the pump beam; and two edge surfaces onopposite sides which are formed by and co-located with the at least oneedge surface of the pump beam and the at least one edge surface of theoutput beam.